Electrical connection and method



June 11, 1957 F. H. WELLS ELECTRICAL CONNECTION AND METHOD Original Filed 001;. 24. 1947 2 Shets-Sheet 1 INVENTOR fma u/v A. #4243.

June 11, 1957 F. H. WELLS ELECTRICAL CONNECTION AND METHOD.

Original Filed Oct. 24. 1947 2 Sheets-Sheet 2 ELECTRICAL CONNECTION AND METHOD Franklin H. Wells, Harrisburg, Pa., assignor to A M P Incorporated, a corporation of New Jersey Original application October 24, 1947, Serial No. 781,826, now Patent No. 2,704,358, dated March 15, 1955. Divided and this application March 15, 1954, Serial No. 420,767

9 Claims. (Cl. 339276) This invention relates to electrical connections comprising electrical conductors with connectors attached thereon, and to methods of forming same.

This application is a division of application Serial Number 781,826, filed October 24, 1947, by Franklin H. Wells, for Electrical Connection and Method, now U. S. Patent No. 2,704,358, issued March 15, 1955.

In the production of all types of electrical equipment, it has been found advantageous to make electrical wiring connections by attaching to the wires or other electrical conductors, connectors which are adapted in turn to make efficient electrical and mechanical connection with electrically conductive elements of the equipment, as distinguished from methods wherein the wires are connected directly to said elements with or without soldering. Where the wires are insulated, that portion of the insulation at the point where the connector is to be attached has had to be removed before attachment except in the case of special terminals having prongs adapted to pierce the insulation and contact the central wire. Stripping of insulation i disadvantageous not only in that costly working time is consumed and special apparatus required, but also in that it frequently result in severing some of the strands of the ordinary stranded conductor wire.

Accordingly, it is among the objects of this invention to provide an efficient method of conductively attaching an electrical connector to an insulated wire without removing the insulation from said wire. It is also an object of this invention to provide such a method which does not depend upon an edge of the connector to cut through the insulation.

Another object is provision of a method of forming electrical connections which is economical and which uti lizes connector blanks and crimping devices of simple and readily available type. A further object is that of providing connections which afl'ord good electrical conduction which is maintained despite subjection to severe physical stress and exposure to corrosive atmospheres and sprays, etc. Other objects will be in part obvious and in part pointed out hereinafter.

In this specification and the accompanying drawings 1 have shown and described a preferred embodiment of my invention and suggested various modifications there of; but it is to be understood that these are not intended to be exhaustive nor limiting of the invention, but, on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings,

Figure 1 is an isometric view of an end of an insulated wire the insulation of which has been slit;

Figure 2 is an isometric view of a typical connector which may be used in the practice of this invention;

Figure 3 is an isometric view of a pair of typical crimping dies which may be used in the practice of this invention, with a. connector and wire in place in the dies before crimping;

Figure 4 is an isometric view of the dies in closed position on the crimped connector;

Figure 5 is a vertical axial section through a modified form of die which may be used in the practice of this invention;

Figure 6 is a transverse section through a crimped connection wherein the insulation is slit along the lower side of the wire;

Figure 7 is a transverse section through a crimped connection wherein the insulation is slit along both upper and lower sides of the wire;

Figure 8 is a transverse section through a crimped connection wherein the insulation is slit along both upper and lower sides of the wire and where the ferrule of the connector has been indented both at the top and bottom;

Figure 9 is an. isometric view of another typical connector which may be used in the practice of this invention;

Figure 10 is an elevational view of another form of crimping die which may be used in the practice of this invention;

Figure 11 is an isometric view of an end of a length of wire from which portions of the insulation have been removed;

Figure 12 is a transverse section through a connector assembly formed by crimping a connector of the type shown in Figure 9 on the end of a wire prepared as shown in Figure 11 with a die such as shown in Figure 10; and

Figure 13 is an isometric view of a connector assembly comprising a connector of the type shown in Figure 2 crimped onto a conductor which has been prepared as illustrated in Figure 11, in accordance with another method within the scope of my invention; for simplicity, the tongue portion of the connector has been broken away.

The first step of forming an electrical connection in accordance with the present invention, comprises breaking into, but not stripping, the insulation in the area where the connection is to be made. In the example illustrated in Figures 1 to 10 this is by the forming of a longitudinal slit 16 in the insulation 18 on the wire 14, as shown in Figure 1.

While in Figure 1 and throughout the several figures of the drawings the connector is shown applied to an end of the wire, the connectors may suitably be applied at any other point along the length of the wire.

Slit 16 may be formed manually, for example, with an ordinary knife, or it may be performed by a machine, e. g. one adapted to stab the wire from opposite sides with slitting knives or chisels, or to pass the wire between rotatingknife disks; or the slitting knife may be incorporated in the crimping die. Slit 16 preferably extends completely through the insulation, although it satisfactorily may be shallower provided it extends deeply enough into the insulation to weaken appreciably that portion of the insulation where the slit is made so that it will start a tear under the stress of crimping and thus expose the wire before the crimping is completed. The length of slit 16 is approximately equal to, or advantageously somewhat less than, the length of theferrule of the connector which is to be applied. 'It is an advantage of the invention thatit provides for locking the insulation and the central conductor together, as well as to the connector, so that they support one another against tensile and bending stresses. This locking is most eiiective when the slit ends well within the crimped portion of the ferrule.

The end of the wire, having been thus prepared by breaking, at least partially through the insulation, is inserted into the ferrule 22 of an electrical connector. The connector illustrated, ,which is shown most clearly in Figure 2, comprises a tubular ferrule 22 and a tongue 24 '22 although it may be appreciably more or less.

which is connected to ferrule 22 by a neck 26 which may be of any usual or special form or omitted altogether. As shown, tongue 24 is provided with a hole 28 for connecting to other electrical components, as by bolting or otherwise. Such connectors may be suitably fabricated, for example, by stamping in one piecefrom sheet metal wherein ferrule 22 is formed of opposed tabs which are rolled upwardly until their ends meet and are brazed to form a peripherally continuous tube, or the ferrule may be deep drawn from the copper strip from which the tongue is stamped.

The end of wire 18 is inserted in ferrule 22 in such manner that the end of the wire projects slightly beyond the end of the ferrule adjacent tongue 24, as shown in Figure 3.

'ever, that the same connector may be employed on wires of a substantial range of sizes, the excess cross-sectional area of the wire being disposed of, at least in part, by compressive extrusion of the resilient or plastic insulating material.

The connector and wire when thus assemble-d are placed between a pair of crimping dies of the type shown in Figure 3. The lower die includes an upstanding rectangular column 30 whose width approximately equals the diameter of ferrule 22 and whose length may be approximately equal to, but advantageously is slightly less than, the length of ferrule 22. The upper face 32 of column 30, which constitutes the lower die face, is shown as a cylindriform trough whose contours are approximately fitted to those of ferrule 22. The form of the die face however can be widely varied, e. g., from fiat, or even convex, to a W or M form.

The upper die comprises a block 34 having a recess in the lower side thereof, said recess having opposed parallel side faces 36 which terminate in an end face formed to an M-shape, with parallel troughs 38 and a ridge 40 extending between troughs 38% along the center line of the die. The width between the side faces 36 is slightly greater than the outside diameter of ferrule 22 and approximately equal to the width of column 30 so that side faces 36 fit over ferrule 22 and column 30. Troughs 38 are approximately cylindriform and substantially tangential to side faces 36, and each has a radius approximately one-half of the outsideradius of ferrule The upper and lower dies may be mounted on the ram and table, respectively, of any standard or special press or may be formed on opposite jaws of a pliers-like hand tool. While the lower die has been shown as the male, and the upper die as the female, these may be reversed.

During closure of the dies, ridge 40 contacts ferrule 22 along the top thereof and turns it inwardly from both turn strikes insulation 18 along slit 16 andwedges apart t the insulation along the slit and contacts the conductive core 20 of the wire.

During this first phase of the crimping the cross-sectional area within ferrule 22 is reduced to equal substantially the cross-sectional area of wire 14 with its insulation; while the shape of wire 14 is deformed and the relative positions of the strands of conductor 20 and insulation 18 are changed with but slight, if any, reduction in cross sectional area of wire 14; past this point, as the dies continue to close, ferrule 22 and its contents are compacted so that each of the strands of conductor 20 are deformed to fill the interstices and form a substantially solid metallic section which contacts ferrule 22 throughout substantially its entire internal surface between the parted edges of insulation 18. At the same time there is a cold flow of the metal in the ferrule whereby the wall is first thickened and then the ferrule is extruded I 4 to greater length. Although such flow relieves stresses in the metal, the interior of the ferrule is maintained at considerable pressure by the compressed resilient insula tion, to give positive engagement of the conductor with the interior of the ferrule.

In Figure 5 is shown in axial section a preferred form of the upper die shown in Figures 3 and 4. In the die of Figure 5, boss 46, which is longitudinally centered in the die, does not extend the full length of the die, leaving at either end a semi-cylindrical portion 48. The use of this die results in indenting only a central portion of the ferrule 22; the wire 14 is deformed only along that portion adjacent the indentation and not along that portion immediately adjacent the ends of the ferrule. This gives the connector assembly a high pull-out resistance and high fatigue resistance against transverse bending. Also since the insulation 18 on wire 14 is separated only along that portion of the wire adjacent the center of ferrule 22 and not along that portion of the wire at either end of the ferrule, the conductor 20 is well sealed against corrosion.

Figure 6 is a transverse section through a connector assembly in which a connector blank of the type previously described is crimped by means of dies, such as those described above, onto a wire which has been prepared as described, the wire, however, being oriented in the ferrule 22 with the slit 16 through its insulation adjacent the bottom, i. e., facing away from the point at which the indentation is made. In crimping, indentation 42 contacts the wire on the side opposite the slit and drives the wire through the slit into compressive engagement with the base.

In either this type of crimp, or that wherein the indentation is made on the slit side of the wire, the wire preferably should be so oriented that the slit in the insulation is within approximately 15 of the axial plane bisecting indentation; this, however, affords a sufficient tolerance that the wire may be rapidly inserted manually or by automatic mechanism under production conditions without extraordinary expense. Advantageously, however, the slit will be made in the same operation as the insertion into the ferrule and the ferrule is crimped in the same location so that the knife or chisel which makes the slit establishes the orientation plane to which the crimp location is related.

In Figure 7 is shown a similar view of a connector assembly wherein the same connector blank and die are used, but where the wire is slit along both top and bottom, the two slits being apart. As shown this results in a crimped connection in which the ferrule contacts the conductor along both top and bottom. Such a connection has a very great area of contact and a high current capacity.

In Figure 8 is shown a similar view of a connector as sembly wherein a connector blank of the type heretofore and bottom and contacts the conductor along both indentations. Three or more indentations may be made as shown, for example, in Patent No. 2,034,090 to Harry A. Douglas, and the insulation slit at one or more or all of the indentations.

In Figure 11 is shown an end of an insulated wire 50, wherefrom portions of the insulation 52 at either side of said wire have been removed along a short distance from said end. Such remova'l may suitably be accomplished by abrasion, as with a standard, coarse, highspeed grinding wheel. The removal is preferably to such depth, as shown, that the conductive core 54 of the wire is just bare'd, as at 58, along'the center of the flattened face 56 formed by such removal. The grinder in such case is provided with stops to limit the grinding to the thickness of the insulation so that wire core wil l'not be substantially weakened or reduced in cross-section. This operation may thus be performed rapidly and without hazard of injury to the conductor 54. This method of preparing the wire for crimping may be used in lieu of slitting in any of the types of connector assembly described above, and of course, may be used on one or more sides of the wire.

Since a portion of the insulation has been removed from the wire, less of the internal sectional area of the crimped connection is occupied by the remaining insulation, and the breach between the parted edges of the insulation becomes wider to allow greater area of contact between the conductor and the internal surface of the ferrule.

In Figure 9 is shown a modified form of connector blank which may be used in the practice of this invention. It is similar in all respects to the blank shown in Figure 2, except that the edges 58 of the opposed tabs 56 which meet in a butt joint along the top of the cylindrical ferrule are not brazed or otherwise made peripherally continuous. The blank shown in Figure 9 may be applied on a slit wire, as shown in Figure 1, with the slit aligned with or opposite to the butt joint, or on a wire from which portions of the insulation have been removed, as shown in Figure 11, in which case the orientation of the wire in the ferrule is not essential.

Suitably, the crimping of the terminal shown in Figure -9 onto either of said types of wire may be accomplished in a pair of dies, the lower of which is similar to the lower of the dies shown in Figures 3 and 4, and the upper of which is shaped as shown in Figure 10. Said upper die comprises a block 60 having in its lower side a recess formed of opposed parallel side faces 62 which merge into an upper face formed to an M-shape, with parallel cylindriform troughs 64 which meet along the center line of the die in a comparatively sharp ridge 66. Troughs 64 are tangential to said faces 62, and their radius is such that they are substantially mutually tangential along the center line of the die. When crimping is accomplished, ridge 66 contacts the ferrule of the connector along the seam formed by edges 58 and turns it inwardly. As closure of the dies continues, at one point tabs 56 will be bent so as to conform to the contour of troughs 64. Past this point, as closure continues, tabs 56 curl around troughs 64, contact wire 50 along exposed portion 55 of conductor 54 and are driven into the bundle of strands forming said conductor, as shown in Figure 12. At the same time the metal of the ferrule is thickened by compression at the inturned ends and at the sides and to a lesser extent even at the top in the troughs 64.

If, as shown in Figure 11, the strands of conductor 54 are spirally twisted to an appreciable extent, the edges 58 may not pass between the strands but will force the uppermost strands downwardly to displace the remaining strands aside and upwardly within the ferrule. If the strands of conductor 54 are not twisted, or are twisted but slightly, edges 58 will part some strands and pass between them. In the latter type of crimping, less crimping force is required. In the former type, more force is required, but, due to the rearrangement of the relative positions of the strands, a connector assembly having an extremely high pull-out resistance is formed. In either case the resulting connector assembly has very high contact area, since a substantial portion of the end of each tab 56 is in contact with the strands of conductor 20.

If the insulation of wire 50 has been removed at both top and bottom, as in the wire shown in Figure 11, conductor 20 will be driven into compressive engagement with the internal surface of the ferrule at the bottom thereof, as shown in Figure 12. This is seldom important, however, since the high current carrying capacity aflorded by contact of the ends of tabs56 with the corl ductor 20 will be suflicient, so that removal of insulation from either the top or the bottom of the wire may be suitably dispensed with. In crimping, the tabs 56 will continue to slide around the troughs 64 until they reach approximatelythe position shown. Past that point, the resistance to further penetration creates sufficient back pressure that frictionbetween tabs 56 and troughs 64 becomes great enough to prevent further sliding. As the dies complete their downward movement, the sides of the ferrule and the down-turned edge portions are compressed and thickened; and the wire within the ferrule is compacted, and to some extent extruded, in the manner hereinbefore described.

In lieu of the type of connector shown in Figure 9, a connector having an open, U-shaped ferrule of the type shown and described in the copending application of James C. Macy, Serial No. 717,842, filed December 23, 1946, may be used. This results in a crimped connection closely resembling that of Figure 2, except that, as pointed out in said copending application, since the ends of the connector tabs in crimping follow approximately arcuate courses, their ends 58' separate within the conductor, to divide the core into three approximately equally sized bundles of strands.

In Figure 13 is shown a connector assembly crimped in an alternative manner within the scope of my invention. In the particular assembly shown, the conductor 50 has been prepared. as shown in Figure 11, and the ferrule 60 of the connector has been crimped in place on the conductor by forming on one side of the ferrule a pair of longitudinally spaced transversely extending flattened portions 62. Such a crimp may preferably be made by using a pair of dies of the type shown in Patent No. 2,379,567 to Stephen N. Buchanan.

The interior of the ferrule in the area of the indentations 66 is driven into compressive contact with the conductive core of the wire and said core is compacted and extruded in the manner hereinbefore described; in the present method, some of the extrusive flow is from the portion of the wire opposite the indentations into that portion between the indentations, creating a protuberance in the latter area, which forms an excellent lock between and among the ferrule 60, insulation 52 and conductive core 54, atfording extremely high resistance to tensile forces. While the method of preparing the wire as shown in Figure 11 is extremely well adapted for the type of crimp illustrated by Figure 13, another suitable method of preparing the wire is that of making one or more slits in the insulation 52, the slits extending transversely of the wire and penetrating just through the insulation, or deeply enough therein to weaken it substantially and allow it to tear apart under the stress of crimping. Preferably, the slits are made adjacent the points where the indentations 62 are to be made, so that the interior wall of the ferrule at the indentation acts to wedge apart the insulation along the slit and allow the greatest area of contact between the ferrule and conductor core 54. Only one, or three or more of such indentations 66 may suitably be made instead of the number shown.

In all of the above embodiments the costly operations necessary to accomplish wire stripping have been eliminated. The connector assemblies formed have excellent electrical characteristics and high strength against tensile pull and high resistance to fatigue and corrosion. There will thus be seen to have been provided methods and devices whereby the aforementioned and other desirable objects may be obtained.

I claim:

1. The method of attaching to an insulated stranded conductor a terminal connector having a tubular ferrule formed of a strip portion the ends of which meet in a butt joint which comprises the steps of removing a portion of the insulation from one side of said conductor adjacent an end thereof, inserting said end into said ferrule,

,7 bending said ends inwardly and driving them radially into engagement with the strands of said conductor in the area where said portion has been removed.

2. The method of making an electrical connection to a conductor having an inner conductive core and an outer insulation sheath comprising the steps of forming a general cylindrical metal ferrule, removing a lengthwise strip of said insulation sheath leaving substantial portions of said sheath in position on the core along each side of the length of the area from which the insulation sheath has been removed, placing said ferrule around said insulation sheath adjacent the area from which the portion of the insulation sheath has been removed, and crimping said ferrule into compressive engagement with said sheath and said core, thereby to press said core into contact with said ferrule along a longitudinal line.

3. The method as claimed in claim 2 including the additional step of removing a second lengthwise strip from said insulation sheath on the opposite side from the area where the other strip is removed.

4. The method as claimed in claim 2 wherein a longitudinally extending portion of said core is exposed by said step of removing a lengthwise strip of said insulation sheath.

5. The method as claimed in claim 2 wherein said metal ferrule is peripherally continuous and wherein said crimping step is accomplished by indentation of said ferrule.

6. The method as claimed in claim 2 wherein said metal ferrule is formed of a strip the ends of which meet 8 in a butt joint and wherein said crimping step is accomplished by bending said ends radially inwardly towards said core.

7. An electrical connection comprising an insulated conductor having a conductive core from which at least one lengthwise strip of insulation has been removed leaving substantial portions of insulation in the area from which the insulation has been removed, a ferrule in surrounding relationship to said conductor in the area from which said insulation has been removed, said ferrule being crimped onto said conductor and being in compressive engagement with said conductive core of said conductor.

8. An electrical connection as set forth in claim wherein said ferrule is peripherally continuous and provides at least one indentation on its surface.

9. An electrical connection as set forth in claim 7 wherein said ferrule is peripherially discontinuous and provides longitudinally extending ends bent radially inwardly and compressively contacting said conductive core.

References Cited in the file of this patent UNITED STATES PATENTS 2,275,163 Thomas Mar. 3, 1942 2,302,767 Hackbarth Nov. 24, 1942 2,379,567 Buchanan July 3, 1945 2,511,806 Macy June 13, 1950 2,600,012 Macy June 10, 1952 2,704,358 Wells Mar. 15, 1955 

